Observability + warming guardrails (Codex)

* client_error details, not just a count: new client_errors table + POST
  /api/client-error (reason/path/user-agent/time) + GET /api/admin/client-errors.
  The boot-seatbelt beacon now sends the reason + path (once per page); the admin
  Overview lists the recent errors so we can tell chunk vs SW vs API vs JS — the
  truth meter for the next day as the new SW propagates.
* Deploy warming now also hits the shell, routes (/play /account /admin), SW,
  version.json, word lists, and icons/logo/font — not just immutable chunks.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_admin.py

@@ -390,3 +390,15 @@ def test_word_pool_admin(tmp_path, monkeypatch):
     # remove the admin-added word
     tc.delete("/api/admin/word/pool/plumb")
     assert "plumb" not in tc.get("/api/admin/word/pool").json()["5"]["added"]
+
+
+def test_client_error_telemetry(tmp_path, monkeypatch):
+    app, api = _make(tmp_path, monkeypatch, admin_email="boss@x.com")
+    anon = TestClient(app)
+    assert anon.post("/api/client-error", json={"reason": "boot-timeout", "path": "/play"}).json()["ok"] is True
+    assert anon.get("/api/admin/client-errors").status_code == 401  # gated
+    tc = _signin(app, api, "boss@x.com")
+    rows = tc.get("/api/admin/client-errors").json()
+    assert len(rows) == 1 and rows[0]["reason"] == "boot-timeout" and rows[0]["path"] == "/play"
+    assert rows[0]["user_agent"]  # captured from the request header
+    assert tc.get("/api/admin/stats").json()["client_errors"]["today"] == 1